Stents are widely used for supporting a lumen structure in a patient's body. For example, a stent may be used to maintain patency of a coronary artery, other blood vessel or other body lumen. One or more stents may be placed in a vascular or non-vascular passage or conduit such as an artery, vein, graft, ureter, urethra, bronchus, esophagus, or other passage. Stents can be placed as a carrier for delivering medications for diagnostic or therapeutic purposes, to facilitate flow of liquids, air, or other substances, or for other reasons as is known in the art.
A stent is typically a metal, tubular structure, although polymer stents are known. Stents can be permanent enduring implants, or can be bioabsorbable at least in part. Bioabsorbable stents can be polymeric, bio-polymeric, ceramic, bio-ceramic, or metallic, and may elute over time substances such as drugs. In some instances, a stent is passed through the body lumen in a collapsed state. At the point of an obstruction, or other deployment site in the body lumen, the stent is expanded to its expanded diameter for its intended purpose.
In certain stent designs, the stent is an open-celled tube that is expanded by an inflatable balloon at the deployment site. Another type of stent is of a “self-expanding”type. A self-expanding stent does not use a balloon or other source of force to move from a collapsed state to an expanded state. An example of a self-expanding stent is a coil structure that is secured to a stent delivery device under tension in a collapsed state At the deployment site, the coil is released so that the coil can expand to its enlarged diameter. Another type of self expanding stent is an open-celled tube made from a self-expanding material, for example, the Protege GPS stent from ev3, Inc. of Plymouth, Minn. Some types of self-expanding stents are made of so-called shape-memory metals such as nitinol. Shape-memory metal stents can self expand when thermomechanically processed to exhibit superelastic material properties. Such shape-memory stents can also self-expand through use of a pre-programmed shape memory effect. Stents processed to exhibit a shape memory effect experience a phase change at the elevated temperature of the human body. The phase change results in expansion of the stent from a collapsed state to an enlarged state.
As is known, a stent is delivered to a deployment site by a stent delivery system. The stent is mounted on a distal end of such a system, the system is maneuvered within a patient's lumen, conduit, or passage and expanded and released at the desired location. There are two main types of stent delivery systems: over-the-wire (OTW) systems and rapid-exchange (RX) systems. In an OTW system a guidewire, used to facilitate navigation or tracking of the stent delivery system through the body, is slideably contained within the full length of the stent delivery system. In an RX system the guidewire is slideably contained within a short distal length of the stent delivery system. RX systems provide certain advantages as compared to OTW systems. RX stent delivery systems use short (typically 170 cm) guidewires which can be handled by one operator, whereas OTW stent delivery systems require long (typically 320 cm) guidewires which must be handled by two operators, increasing procedural cost and complexity.
While an RX system may provide advantages over an OTW system, the RX system presents some issues of its own that must be considered. For example, it is important for the stent delivery system to slide easily over the guidewire so that the stent can be easily tracked over the guidewire to the intended stent deployment site. If the components of the stent delivery system are not properly aligned there can be friction against, or entanglement with, the guidewire. In some situations, guidewire interaction issues such as these can prevent the stent delivery system from tracking to the intended stent deployment site, or can even prevent deployment of the stent after the site is reached.
Because of the tortuous pathway in the body and the torqueing of the delivery system during advancement to the deployment site, it is important to maintain an orientation between a guidewire lumen located within an inner member in a medical delivery system and an RX port. If this orientation is lost, it may not be possible to mount the delivery system on the guidewire or it might take too much time. Any delays may be detrimental to the patient. Further, if the needed orientation is lost, it may not be possible to track the stent to the intended deployment site, or to deploy the stent.
Accordingly, a need exists for a medical implant delivery system which is capable of maintaining proper orientation between coaxially slidable members of the system, particularly with reference to the rapid exchange guide wire lumen and the deployable device carried by the delivery system.